A liquid crystal display generally includes a backlight device and a liquid crystal panel. The backlight device is constructed of a sheet metal back chassis, a sheet metal front chassis, a light reflecting plate, a light source supporting section, a light source, a light diffusing plate, a light guide plate used as required, and a light source drive circuit such as an inverter. The liquid crystal display has a structure in which a liquid crystal panel is arranged and fixed on the backlight device. The backlight device is roughly classified into three types of a direct type, a light guide-type, and a tandem-type which is a hybrid of the two types. Of those, a backlight device to be used for a large screen liquid crystal TV requires high brightness, and thus a direct type- or tandem (hybrid) type-backlight device has recently been developed actively.
Structure of a Direct Type-Backlight Device
A conventional direct type-backlight device is constructed of a flat or corrugated light reflecting plate formed by bonding and laminating a resin foam on an aluminum sheet metal substrate, a plurality of light sources, a light source support, a light diffusing plate, a plurality of optical films, sheet metal chassis (a back chassis and a front chassis), and the like (see Patent Documents 1 to 3, for example).
Structure of a Tandem (Hybrid) Type-Backlight Device
A conventional tandem type-backlight device is constructed of a light reflecting plate formed by bonding and laminating a resin foam on a wedged aluminum sheet metal substrate or a plurality of light reflecting sheets, a plurality of light sources, a light source support, a light diffusing plate, a plurality of light guide plates, a plurality of optical films, sheet metal chassis (a wedged back chassis and a front chassis), and a light source electrode terminal cover as required (see Patent Documents 4 and 5, for example).
A conventional liquid crystal display is constructed by arranging a liquid crystal panel on the backlight device.
A reflecting plate to be used is obtained by bonding and laminating a resin foam on an aluminum sheet metal substrate as shown in FIG. 9 for preventing warping and deformation of the reflecting plate and maintaining a structure thereof. In general, a reflector is produced through sheet metal working such as press working for a corrugated shape or folding for forming a side surface.
A plurality of light sources is used in accordance with a display screen size of a liquid crystal display and brightness required for a backlight device. A point light source such as a linear or U-shaped cold cathode tube (CCFL) or an optical semiconductor device (LED), or a light source including linearly or flatly arranged point light sources is used as the light source.
A light source support is not formed of a sheet metal, and an injection molded product of a thermoplastic resin composition is often used. In particular, a light source support molded by using a polycarbonate resin composition containing titanium oxide has a light reflecting function, and a light source support having a structure in which a rib structure is formed outside of the light supporting function for improving torsional rigidity of the light reflecting plate is employed.
A light diffusing plate is generally obtained by using an acrylic resin, an acrylic monomer/styrene copolymer resin, or a polycarbonate resin. In these days, a light diffusing plate is obtained by using a resin composition containing a light diffusing agent mixed into a transparent resin such as a cyclic olefin resin. The light diffusing plate has a thickness of about 1 to 3 mm and is selected in accordance with a liquid crystal display screen size or a lighting system.
In addition, not only a light source supporting section but also a light diffusing plate supporting frame may employ a frame having a rib structure formed of an injection molded product of a polycarbonate-based resin composition containing titanium oxide.
An optical film having a plurality of functions is laminated. In general, a light diffusing film to be used for providing uniform surface brightness of a backlight device or a prism sheet having a brightness enhancing function is used. A plurality of those optical films is laminated and used for adjusting the brightness and uniformity of the brightness.
A light guide plate is generally obtained by using an acrylic resin or a polycarbonate resin. In these days, a light guide plate is obtained by using a transparent resin having high light guide property such as a cyclic olefin resin, and is selected in accordance with a use environment or a screen size. The light guide plate has scattering patterns or fine irregularities on a back surface of the light guide plate which are formed with light diffusing white ink or the like, and is a light transforming element for uniform and efficient surface emission of light entered from a linear light source or a point light source in a light exiting direction.
Those conventional backlight devices each have a large number of components and many assembly steps. Further, sheet metal working is conducted twice for producing a reflector by corrugating the light reflecting plate or folding for forming a side surface of the light reflecting plate, and for producing a chassis (casing). Thus, assembly of the backlight device requires double steps, and increase in weight of an entire device is inevitable. In the light reflecting plate obtained by bonding and laminating a resin foam on an aluminum sheet metal substrate, a resin foamed layer is liable to peel off from the aluminum sheet metal substrate during sheet metal working and position shift may be caused. Thus, sheet metal working of a complex shape involves difficulties. The aluminum sheet metal substrate to be used herein is formed of aluminum or aluminum alloy. However, an easily available and relatively inexpensive aluminum material of 52S cannot be used for imparting sheet metal working properties, and an expensive material must be used. As described above, sheet metal working of a complex shape involves difficulties, and thus a reflector must be produced by: producing a light source support having a structure for preventing torsion and reinforcing a light reflecting plate and having functions of supporting a light source, supporting a reflecting section, insulating heat of a light source electrode terminal, and the like by using a resin composition by a separate injection molding method and attaching and fixing the light source support after the light source is provided to the light reflecting plate. In the case where the aluminum sheet metal is used, a thickness of a chassis is 1 mm with a display screen size of 22 inches, 1.5 mm with a display screen size of 30 inches, and 2 mm with a display screen size of 40 inches, which also causes weight increase (see Patent Documents 6 and 7, for example).
There is proposed a sheet metal substrate provided with a coat having light reflecting property on a sheet metal substrate for a light reflecting plate in advance. However, the sheet metal substrate is applied to the light reflecting plate alone, and no reflector having a structure provided with a back chassis and/or a light source support is proposed. Thus, a light source support produced by the separate injection molding method must be applied to a light source supporting section as described above.
Meanwhile, in the case where a light reflecting plate is formed by using a polycarbonate-based thermoplastic resin composition containing titanium oxide and having a light reflecting function without using the aluminum substrate, suppression of warping and deformation caused by thermal expansion with temperature increase by heat from a light source involves difficulties.
Further, for formation of a chassis for supporting a liquid crystal panel as required, rigidity is hardly ensured (see Patent Documents 8 and 9, for example).
There are proposed methods of improving a structure of a light source electrode terminal, which is a source of heat generation, and enhancing heat radiation property, but the methods do not reduce the number of components (see Patent Documents 10 to 12, for example).
Patent Document 1: JP-A-2004-22352
Patent Document 2: JP-A-2004-127643
Patent Document 3: JP-A-2001-215497
Patent Document 4: JP-A-2003-346537
Patent Document 5: JP-A-2002-72204
Patent Document 6: JP-A-2004-55182
Patent Document 7: JP-A-2004-139871
Patent Document 8: JP-A-2004-102119
Patent Document 9: JP-A-2003-162901
Patent Document 10: JP-A-2004-134281
Patent Document 11: JP-A-2001-216807
Patent Document 12: JP-A-2003-234012